Prenatal intoxication of methylmercury has been demonstrated clinically to cause brain damage of human fetus resulting in varieties of cerebral palsy syndromes including mental retardation. This research proposes to study the effects of methylmercury on the growth and development of fetal brain. The overall objectives of this proposal are to assess in detail the changes in development of fetal brain brought about by maternal intoxication of methylmercury, particularly the changes in the pattern of cell proliferation, neuronal migration, cortical differentiation and organization of cerebrum and cerebellum; to ascertain as fully as possible the mechanisms whereby these changes are brought about; and to correlate the findings with alterations observed in some of the developmental disorders of the nervous system encountered in man.